Spinal cord injury severs the connections between the brain and the spinal cord, which causes devastating outcomes such as loss of sensory and motor controls below the lesion site. The reason behind the permanent neurological deficit is that adult mammalian neurons fail to regenerate after injury. One strategy for successful axon regeneration is to enhance the intrinsic axon growth capability of injured neurons. This requires defining molecular pathways that can promote axon outgrowth and establishing therapeutic approaches to turn them on. Recently, we have demonstrated a key role of Smad1, a transcription factor, in switching adult sensory neurons into an active growth state in vitro. This proposal focuses on the in vivo function of the Smad1 pathway using rodent models of spinal cord injury. We propose to test the central hypothesis that activation of Smad1 in adult sensory neurons promotes axon regeneration of ascending sensory pathway. This hypothesis is supported by our pilot studies that demonstrate robust sensory axon regeneration with activation of Smad1 in DRGs. This was achieved using a minimally invasive and clinically applicable in vivo gene manipulation method designed in my laboratory specifically for in vivo spinal cord research. Based on these exciting results, Aim 1 will investigate the Smad1 activation mechanisms in DRG neurons. This includes BMP-dependent and -independent pathways. The role of a novel kinase, Mps1, in mediating axonal growth and the function of the differential phosphorylation of Smad1-at the linker area and C- terminus will be studied. The downstream targets of Smad1 will be identified. Aim 2 focuses on in vivo assays using rodent models of spinal cord injury to compare the regenerative phenotypes of Smad1 activation by BMP-dependent and -independent pathways. Therapeutic potential of AAV-BMP will be further evaluated by injecting AAV after injury. In summary, these studies are expected to provide insights into the therapeutic potential of manipulating the Smad1 pathway on axon regeneration after spinal cord injury. Furthermore, this proposal also aims at identifying novel molecular targets that activate Smad1 or act as downstream effectors. Finally the in vivo studies will validate a minimally invasive and clinically applicably therapeutic approach that can be readily translated into clinical trials for spinal cord injury patients.